This is a description of the method used to measure the flux-based(temporal) droplet size distribution for
atomizers used in the aerial application of pesticides in agriculture and forestry. Figure 1 shows a sketch of the
circular cross-section wind tunnel (1.02 m in diameter)used for this. The Malvern 2605C laser Fraunhofer
diffraction instrument is installed so that the laser beam crosses the wind tunnel horizontally (through apertures
in the wall) on a diameter of the tunnel cross-section, with transmitting and receiving modules fixed on pylons
independent of the tunnel structure. Atomizers are fixed on a vertical boom which is located on a diameter of the
tunnel cross-section upstream of the laser beam. Testing is conducted by releasing the liquid stream through the
atomiser into air flowing through the tunnel. Air velocity in the tunnel exhibits a square profile upstream and a
short distance downstream of the atomizer, and is set at a value equal to aircraft airspeed.

A total spray plume traverse is done by making measurements at each of a series of laser beam transects
(along a chord) across the plume, separated by a vertical spacing of 1 or 2 inches (2.5 or 5.1 cms), depending on
the size of the plume, from upper to lower plume edges. For axially symmetric plumes (e.g. from rotary
atomizers), it is sufficient to carry the sampling from the center of the plume to one edge.